The present invention relates to an optical detector comprising a system for emission and reception capable of generating a pulsed emission electrical current and consequently of emitting a pulsed optical beam towards an object, and able to treat, by means of an electronic receiver circuit, a voltage signal received which is produced by the pulsed optical beam returned by the object according to the presence and/or distance of the object.
It is known from prior art that optical detectors, in particular background suppression optical cells, generate a reception voltage signal which can vary widely depending on whether the object detected sends back a low or high fraction of the energy emitted. Thus, for example, one needs to be able to raise the luminous intensity of emission in the presence of an object sending back little light. Besides, in the electronic circuits of such optical cells, it is necessary to avoid saturation of the amplification chains of the channels, this saturation disturbing detection, and thus it is advisable to be able to reduce the luminous emission intensity.
It is known from prior art how to use means of regulation of the emission current in the system of emission and reception of the optical cell, these regulation means varying the level of energy emitted through modification of the emission frequency of the current impulses. But, for certain types of cells, it may be necessary to retain an unchanged emission frequency, and the regulation means in question will then be unusable.
The aim of the invention is to regulate rapidly the emission current of an optical detector, in particular an object detection optical cell by triangulation, especially with background suppression, while conserving a stable transmission frequency of current impulses.
According to the invention, the means for transmission current regulation detect the value of the voltage signal received relative to a predetermined maximum voltage value and a minimum voltage value, these values defining a regulation interval as well as, on either side of this interval, a high voltage zone and a low voltage zone; on the other hand, the means of regulation are combined in such a way that, when the voltage signal received is situated in the regulation interval, the emission current is regulated by control means in such a way as to bring in and maintain the voltage signal received at a required value and that, when the voltage signal is situated in the upper zone or respectively in the low voltage zone, the emission current is multiplied (or divided) by a predetermined factor, such that the voltage signal is rapidly centred in the regulation interval, and then regulated by the control means.
The combination thus carried out for rapid correction and control is especially efficient. To begin with, a wide deviation of the received signal brings about an increase or decrease of the amplitude of the emission current, by a significant factor, which leads the received voltage signal during the regulation interval, then after that the final regulation of the emission current brings the received voltage signal to the required value. Through the first phase of quasi-exponential centring, the regulation operation is carried out very rapidly, that is to say within several emission cycles and in any case for a lower number of cycles than with prior art detectors.
The predetermined factor is at the most equal to the ratio of maximum and minimum voltage values or respectively minimum and maximum, for example of the order of 4 or xc2xc.
The control means can advantageously be constituted by a digital analog converter combined or not with a microcontroller which calculates the level of the emission current. The latter then generates impulses of modulated width applied to an integrator element, in such a way as to create an analog signal which defines an emission current making it possible to reach the required voltage value.